Internalizing disorders, consisting of syndromes of anxiety and depression, represent common, debilitating conditions, the etiology of which is not well understood. Neuroscientists have developed dimensional assessment instruments and psychological tasks that probe negative valence systems as alternative phenotypes to clinical symptoms. Such alternative phenotypes are under consideration for use in the NIMH's Research Domain Criteria (RDoC) project. However, little is currently known regarding their genetic basis and how that relates to internalizing risk factors. This study will extend and deepen our understanding of the relationships between such alternative phenotypes and early manifestations of ID symptomatology. The approach will be to administer an informative suite of dimensional measures and experimental tasks to 500 pre-adolescent twin pairs from a large epidemiological sample. These subjects will also be assessed for current and lifetime internalizing psychopathology and a broad array of childhood risk/ protective factors. The expected outcome is to provide novel insights into the mechanisms by which genes and environment confer risk to internalizing disorders via these more basic phenotypes that putatively reflect underlying affective processing.